Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Dec. 31, 2011	$ 552,980	$ 84	$ 135,668	$ 434,581	$ (17,353)
Balance, Shares at Dec. 31, 2011	42,223	42,223
Issuance of common stock under stock option plans	15,579	2	15,577
Issuance of common stock under stock option plans, shares	745	738
Stock-based compensation expense	6,795		6,795
Excess tax benefit from stock option exercises	3,256		3,256
Payment of dividends	(13,706)			(13,706)
Net income	51,854			51,854
Net unrealized gain on available-for- sale investments, net of tax of $302	730
Foreign currency translation adjustment, net of tax of $180	(12,086)				(12,086)
Balance at Sep. 30, 2012	$ 605,402	$ 86	$ 161,296	$ 472,729	$ (28,709)
Balance, Shares at Sep. 30, 2012	42,961	42,961